The invention relates to a circuit for generating a sine wave for an automotive appliance antenna.
Antennas of automotive appliances are driven through a power H-bridge by a low distorted carrier sine wave. FIG. 1 shows diagrammatically a prior art circuit for such an antenna. The antenna 1 is driven by a power bridge circuit 2, comprised of four power transistors 4, 6, 8 and 10 mounted on a printed circuit board 12. The circuit is a discrete component power bridge, this being symbolized in FIG. 1 by the boxes around each of the transistors. In a way known per se, the emitter of transistor 4 is connected to the emitter of transistor 6, thus forming a first leg of the H-bridge. The emitter of transistor 10 is connected to the emitter of transistor 8, thus forming a second leg of the H-bridge. The antenna is connected to the middle section of both legs of the H-bridge circuitxe2x80x94that is on one hand between transistors 4 and 6 and on the other hand between transistors 8 and 10. The top section of both legs of the H-bridgexe2x80x94that is the collectors of transistors 4 and 10xe2x80x94is connected to power supply 16, whereas the bottom section of both legs of the H-bridge circuitxe2x80x94that is the collectors of transistors 6 and 8xe2x80x94is connected to one terminal of a sense resistor 18, the other terminal of which is grounded. Thus, sense resistor 18 receives a voltage image of the current applied to antenna 1.
FIG. 1 further shows an integrated circuit 20, comprising a regulator 22 and a sine wave generator 24. The one terminal of the sense resistor 18 is connected to one pin of the integrated circuit, and is inputted to the regulator 22. The regulator also receives on another pin of the integrated circuit a reference signal SETP representative of the amplitude of the signal to be applied to the antenna. The regulator outputs to the sine generator a SET signal representative of a difference between the voltage across sense resistor 18 and the reference signal SETP.
Sine generator circuit receives the SET signal, and digital inputs DIG-IN representative of the frequency of the sine wave to be applied to the antenna. Based on the SET signal and on these inputs, the sine generator outputs four control signals respectively applied to the bases of the transistors 4, 6 and 8, 10 forming each leg of the H-bridge circuit.
The operation of the circuit of FIG. 1 is the following. As explained above, sense resistor 18 receives a voltage image of the current applied to antenna 1; voltage across sense resistor 18 is compared in regulator 22 to reference voltage SETP so as to control amplitude of the sine wave output by sine generator 24. Frequency of the sine wave is controlled by the digital inputs to regulator 22. FIG. 1 does not show the circuits for modulating the sine wave carrier applied to the antenna.
Typical values of voltages and powers in the circuit of FIG. 1 are the following. Power supply SUPP 16xe2x80x94the automotive appliance batteryxe2x80x94usually outputs a voltage below 16 V. Antenna 1 has a resistance between 5 and 15 ohms, and its current may reach 0.5 A. Power dissipation in the H-bridge circuit is around 6 W. It is also required that the sine wave for driving the antenna be a low distortion signal. The rejection for the second harmonic frequency is preferably higher than 30 dB, while the rejection for the third harmonic frequency and higher harmonic frequencies is preferably higher than 35 dB.
The design of FIG. 1 causes a number of problems. First, there is a need to assemble the different components of the power H-bridge on the printed circuit board PCB, and then a need to assemble the power H-bridge with the regulator and sine generator chip, and with the load. These steps of assembly increase the costs of the antenna circuits. Second, the power transistors mounted on the PCB are separate components, and may hardly be matched; this increases power consumption, notably due to quiescent current of the H-bridge at crossover. Moreover, such discrete implementation is prone to reliability problems due to potential connection failures.
In view of high power dissipation in the H-bridge circuitxe2x80x94around 6 W and in any case higher than 3 Wxe2x80x94there is a general prejudice in the art against assembling all components of the circuit on a single die; more specifically, there is a prejudice against using an integrated component for the H-bridge circuit.
The invention addresses these problems. It provides a simple solution, in an integrated circuit. Mounting all components of the circuit on a single die addresses the problems of assembly costs and reliability problem encountered in the prior art solution as mentioned above. In addition, integrating transistors of the H-bridge circuits allows the transistor to be matched. Quiescent current at crossover is better controlled, and current amplitude may be set more accurately.
European patent application with patent application number 99402881.9 filed before the present application but published after the filing date of the present application discloses a sine wave generator for providing a high power and low distortion current sine wave. The generator disclosed in this document comprises a load feeding power bridge connected to the output of a sine wave generator, and a regulator inserted between the feedback output of the power bridge and a reference voltage input of the sine wave generator. The regulator includes regulation means providing a power regulation signal to the reference voltage input of the sine wave generator; the regulation signal is derived from the comparison between a signal at the feedback output of the power bridge and a set point signal. In this application, the regulator is a proportional integrating differentiating regulator; it includes start-up and/or shut-off envelope controlling means, as well as regulation means for obtaining a tightly controlled start-up and/or shut-off slope(s) of the signal at the load feeding output of the power bridge in addition to a tight control of the signal envelope between a start-up slope and the following shut-off slope. The regulator of this document is not necessarily integrated on a single die.
The invention provides a high power sine wave carrier circuit, comprising a power bridge connected to the output of a sine generator, a regulator connected to a feedback output of the power bridge and providing a driving signal to the sine generator, wherein said power bridge, said sine generator and said sine regulator are integrated on a single die, and wherein said circuit further comprises a shutdown pin.
The invention further relates to such a high power sine wave carrier circuit wherein the sine wave at the output of said power bridge has a rejection higher than 30 dB for the second harmonic frequency and a rejection higher than 35 dB for the third and higher harmonic frequencies.
A further characteristic feature of such a circuit is that the power of the sine wave at the output of said power bridge is higher than 1 W.
Another characteristic feature of the circuit is that the internal power of the circuit is higher than 1.5 W.
Yet, another characteristic feature of such a circuit is that, the shutdown pin controls operation of said power bridge, said regulator and said sine generator.
Still another feature is that the power bridge is a H-bridge.
Another feature of the circuit is that the power bridge is a push-pull bridge with matched transistors.
Furthermore, the invention provides a process for applying a high power sine wave to a load connected to the output of a power bridge of a circuit according to one of previous circuits, comprising the steps of powering and shutting down the circuit, wherein:
the duty cycle between said powering and shutting down steps is determined according to a maximum average temperature of the die;
the maximum duration of a powering step is determined according to temperature at any point within the die; and
in any time period equal to the ratio of said maximum duration to said duty cycle, the energy applied to the circuit is less than an upper limit, said upper limit being the energy applied to the circuit by a powering step of said maximum duration.
The process further comprises that the duty cycle is equal or less than:             θ      ⁢      max        -          θ      ⁢              xe2x80x83            ⁢      air            R    ·          (                                    I            0                    ·                      V            supply                          +                              I            load                    ·                      (                                          V                supply                            -                              V                load                                      )                              )      
where l0 is the internal current in the circuit, Vsupply is the voltage applied to the circuit, lload is the RMS value of the current in the load in a powering step, Vload is the RMS value of the voltage across the load, R is the thermal resistance between the die and the air around the die, xcex8max is the maximum average temperature of the die, and xcex8air the temperature of the air around the die.
The process further comprises that the maximum duration of a powering step is determined so that the temperature at any point within the die is less than a maximum operating temperature.
Finally the process comprises that the maximum duration of a powering step is determined so that the temperature at the power bridge within the die is less than a maximum operating temperature.
It is to be noticed that the term xe2x80x98comprisingxe2x80x99, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression xe2x80x98a device comprising means A and Bxe2x80x99 should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noticed that the term xe2x80x98connectedxe2x80x99, also used in the claims, should not be interpreted as being limitative to direct connections only. Thus, the scope of the expression xe2x80x98a device A coupled to a device Bxe2x80x99 should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.